Abstract Distinct cellular reservoirs of replication competent HIV/SIV that are not eliminated by ART are concentrated in lymph node (LN) B cell follicles (BCF) and T cell zones. Optimizing antiviral activity in lymphoid tissues is of critical importance for HIV eradication/remission strategies; however, tightly regulated immune cell trafficking render this challenging. Cytolytic effector T cells are typically excluded from LNs by relative lack of LN and BCF homing receptors and they fail, once entering, to remain as they move into systemic circulation drawn by a concentration gradient of sphingosine-1 phosphate (S1P). To counteract these mechanisms, we recently showed that treatment of ART-suppressed, SIV-infected rhesus macaques (RMs) with the S1P receptor modulator fingolimod is safe and retains cytolytic immune cells in LN. Furthermore, we showed that administration of heterodimeric interleukin-15 (hetIL-15) to uninfected and SHIV-infected RMs promotes expansion of cytolytic CD8+ T cells and NK cells, and promotes their migration to the BCF where infected T follicular helper cells persist. Fingolimod is FDA approved for multiple sclerosis and hetIL-15 is in clinical trials for cancer and HIV. Our findings have provided rationale for two upcoming clinical trials in acute HIV infection, testing the safety of fingolimod or hetIL-15 administration as monotherapies at ART initiation. We propose to move the field forward by exploring the safety and mechanisms of action of a combined fingolimod and hetIL-15 treatment administered with ART in acute SIV infection. We hypothesize that these agents will synergize to enhance SIV-specific defenses in LN, at a time when these defenses are robust; decrease SIV reservoir size; and promote viral remission after ART interruption. Using the highly relevant model of SIV-infected, ART-treated RMs, we will first determine the safety, mechanisms of action, and immunological impact of the single and combined FTY720 and hetIL-15 interventions (Aim 1). If our hypothesis is correct, the proposed studies will provide in vivo evidence of the synergy of FTY720 and hetIL-15 in decreasing virus reservoirs, both in circulation and in lymphoid tissues during ART (Aim 2), and promoting delayed viral rebound and/or durable control of SIV replication after analytical treatment interruption (Aim 3). The proposed studies will be conducted in the most relevant preclinical model of HIV infection; using two molecules that are either approved by the FDA (fingolimod, for multiple sclerosis) or being tested in clinical trials (hetIL-15). Our studies are necessary to provide insights into the safety and mechanisms of the combination to ascertain if such a strategy is safe and plausible for testing in people living with HIV. We believe that the proposed studies are innovative and higly significant to the HIV cure agenda.